The Danube is the second longest river in Europe, after the Volga in Russia. It flows through much of central and southeastern Europe, from the Black Forest to the Black Sea.
A large and historically important river, it was once the frontier of the Roman Empire and today connects ten European countries, crossing their territories or being a border.
Originating in Germany, the Danube flows southeast for 2,850 km, passing or bordering Austria, Slovakia, Hungary, Croatia, Serbia, Romania, Bulgaria, Moldova and Ukraine. Among the many cities on the river are 4 European capitals: Vienna, Budapest, Belgrade and Bratislava.

So the Danube is the playground for many different types of European paddlers. From occasional or recreational athletes to professionals, everyone shares the waters of the Danube.

But how long does it take to paddle the Danube?

It depends is the right answer. And it depends on many factors, but there are two things that we cannot ignore: Speed and Time.

From this we can create two scenarios:

1 Scenario
An unrealistic non-stop paddling session 24/7.
Imagine that you never stop, not to rest, not to eat, not even for anything else. Nothing just paddling along the way starting in Germany and only stopping in Romania.

Persona 1
Beginner level
Average Speed: 8Kmh
Km per day: 192Km (24h X 8kmh)
Duration: 15 days (approx.)

Persona 2
Intermediate level
Average Speed: 12Kmh
Km per day: 288Km (24h x 12kmh)
Duration: 10 days (approx.)

Persona 3
Advanced level
Average Speed: 15Kmh
Km per day: 360Km (24h X 15kmh)
Duration: 8 days (approx.)

2 Scenario
A workable 2/5 sessions.
That means you paddle two hours a day for five days (weekend off).

Persona 1
Beginner level
Average Speed: 8Kmh
Km per day: 16Km (2h X 8kmh)
Duration: 178 Days (approx.)

Persona 2
Intermediate level
Average Speed: 12Kmh
Km per day: 24Km (2h x 12kmh)
Duration: 119 days (approx.)

Persona 3
Advanced level
Average Speed: 15Kmh
Km per day: 30Km (2h X 15kmh)
Duration: 95 days (approx.)

In short, in a realistic plan, it will take from 25 to 13 weeks, depending on your condition, to paddle across the entire Danube.
Granted, it’s just a hypothetical scenario, but as we’ve said before, it’s all about speed and timing.

source: https://en.wikipedia.org/wiki/Danube